The present invention relates to a ceramic material or veneering metallic dental prostheses formed of low-melting gold alloys or titanium with a processing temperature of 770.degree. C. .+-.70.degree. C. and with a coefficient of thermal expansion, .alpha., between 20.degree. and 500.degree. C. of 8.multidot.10.sup.-6 K.sup.-1 to 17.5.multidot.10.sup.-6 K.sup.-1 which can be adjusted to be compatible with particular dental alloys.
Ceramic layers have been used as a veneer to form an enamelling of underlying metallic supporting frameworks (crowns, bridges) for many years in the field of dentistry in order to achieve a natural appearance of the dental prosthesis. For this, ceramic powders are applied as an aqueous slip onto the metallic framework and fired at high temperatures. It is important in carrying this out that the firing temperature (processing temperature) of the ceramic mass is at least 100.degree. C. below the solidus temperature of the material of the metal framework. Also, it is important that the coefficient of thermal expansion of the ceramic mass in the range of 20.degree. to 500.degree. C. is slightly less than that of the metal material in order that no tears occur in the veneering layer during the firing operation and later during the cooling period.
Gold alloys with gold contents between 70 and 85% have recently been used in the field of dentistry which exhibit coefficients of thermal expansion between 16 and 17.5.multidot.10.sup.-6 K.sup.-1. In addition, titanium materials are used with coefficients of thermal expansion between 9 and 10.multidot.10.sup.-1 K.sup.-1. Moreover, these gold alloys exhibit solidus temperatures in a range of 870.degree.-940.degree. C. It is important in the case of titanium materials to remain below the phase transition temperature of approximately 880.degree. C. during the firing operation.
Ceramic masses which cover such a broad range of the coefficient of thermal expansion and exhibit at the same time a processing temperature in a range of approximately 700.degree.-840.degree. C. have not been known in the past.